The invention relates to an improved brush system for an electric motor device which is virtually immune to motor vibration and which facilitates assembly into a motor housing both at the time of motor assembly and later, in the event that servicing is required.
The brush system for an electric motor device will normally include a conductive tubular sleeve mounted in the housing of the motor. This sleeve will be insulated from the housing if the housing is made of metal. It has long been the practice to connect a lead from the motor to this tubular sleeve with the aid of a brass clip which is pre-wired to the motor lead. The brass clip snaps onto the tubular sleeve and is tension-held thereon. Often the connection is obtained by a nut threadably engaging the tubular sleeve and holding a lug to the tubular sleeve.
In electric motor devices this and similar arrangements have lead to serious problems because of the vibration which accompanys operation of the motor device. This is especially true in portable electric power tools such as hammer drills and the like wherein the electric motor of the tool is subjected to continuous vibration during use. The vibration causes relative movement of the clip and sleeve which in turn causes wear and generates heat. These combine to reduce the forces attaching the clip to the sleeve which results in intermittent contact. Once physical separation begins, electrical arcing occurs which generates further heat and errosion of the parts until the system disentegrates with the result that an entire new brush system must be installed. Often, the commutator of the motor too is irreparably damaged and must either be re-cut or entirely replaced.
A similar sequence of events can occur during normal wearing out of a brush, that is, increased arcing of the worn out brush generates heat in the clip area which weakens the clip causing arcing between clip and sleeve and subsequent errosion of both parts such that they must be replaced along with the brushes. On the other hand, it has been found that screws or other threaded members utilized in lieu of clips also present difficulties because they tend to loosen because of vibration.
The above-described brush systems of the prior art require a costly and time-consuming assembly procedure when the brush system is mounted in the housing of the electric motor during manufacture of, say, a portable electric tool. Specifically, the electric clip or lug is secured by hand to the conductive sleeve and this manufacturing step requires intricate manual movements because the assembly often must be made within the interior of a small motor housing. Also, when it comes time to service the motor, the service personnel must likewise diassemble and assemble the brush system within the housing of the tool.